用运放作倒相的EL84推挽立体声放大器

本文介绍一款前级采用运算放大器作倒相放大,输出级采用MT管EL84的推挽立体声功率放大器.该放大器具有体积小、成本低、电路简单、制作容易、初学者也能制作的优点.前级采用运算放大器的目的是减小失真,扩展带宽.用双运算放大器组成两级倒相放大级,EL84采用自给偏压电路,为推挽输出无负反馈放大器.该机失真率小于3%(6～12 W),频带为20Hz～80kHz(1W),最大输出功率达12W.     

用运放作倒相的EL84推挽立体声放大器

本文介绍一款前级采用运算放大器作倒相放大，输出级采用HT管EL84的推挽立体声功率放大器。该放大器具有体积小、成本低、电路简单、制作容易、初学者也能制作的优点。前级采用运算放大器的目的是减小失真，扩展带宽。用双运算放大器组成两级倒相放大级，EL84采用自给偏压电路，为推挽输出无负反馈放大器。该机失真率小于3茗（6-12W），频带为20Hz～80kHz（1W），最大输出功率达12W。     

制作简单、性价比很高的10W功率放大器——日本’94自制放大器竞赛参赛作品介绍

本文介绍的是一款制作非常容易,调整方便、性能好、价格低的10W 功率放大器。在本年度日本自制放大器竞赛中荣获大阪赛区第八名。一、电路特点该放大器的电路如图1所示。该电路是由单端推挽(SEPP)电路演变而来的。在电路中对输出晶体三极管的激励方式作了改进,用两个运算放大器分别驱动两只担任互补推挽输出的功率放大管,两只功率放大管通过发射极电阻相连,扬声器接在发射极电路中。该放大器电路与以往的 SEPP 电路(图2)在下面四个方面有所不同。(1)不需要偏置电路。(2)用运算放大器的输出直接驱动功率放大管。(3)偏置电压的稳定度极高。(4)不需要静噪电路。下面就这四个不同点加以说明。在该电路中由于使用了两个运算放大器,运算放大器本身兼作输出电平的     

用电流反馈放大器作简单的振荡器

用电流反馈型运算放大器生成的高频正弦波,其振幅比用常舰运算放大器的要大。图1所示电路用四个无源元件联接一个电容器以补偿结点(另一种有这个插脚的运算放大器是OP660)。振荡的要求是R_2/R=C_1/C_2。振荡频率(弧/秒)等于。请注意R_2和R_1分别独立地调整振荡幅度和振荡频率。     

线性光耦HCNR201原理及其在轴承故障检测中的应用

因铁路货车轴承故障检测现场工况复杂,各种电磁干扰信号极易随被测信号进入测量系统.针对这个问题,设计了用高线性度模拟光耦HCNR201和运算放大器实现的电压隔离硬件电路.该电路中,线性光耦的前端用一个运算放大器构成一个负反馈放大器,用来检测模拟电压信号;线性光耦后端的运算放大器进行电流与电压之间的转换,最终输出电压信号,实现电压信号的1：1隔离传输.实验结果表明：该方法测量电压线性度好、精度高.     

基于APD的光电探测器电路研究与设计

提出将APD与前置放大器电路配合使用的最佳方法.利用光电转换信噪比数学模型,确定选择与APD匹配的电路器件,给出了前置放大器采用低噪声的分体器件与集成运算放大器相组合的设计方法.通过对前置放大器重要参数信噪比进行测量和分析.结果表明,该探测器电路信噪比优于直接与集成运算放大器匹配的探测器电路,且可靠性高,宜扩展,具有广泛的应用前景.     

单运算放大器绝对值放大电路

本文介绍一种绝对值放大电路,该电路只用一个运算放大器F007便可完成取绝对值和放大的功能.电路如下图所示. 当V_4>0时,D_1导通,D_2截止, V_b=(2KV_i)/(2K+1)-V_(be) 式中V_(be)为微小电流下(运算放大器偏置电流)的二极管正向压降.忽略失调电压和失调电流的影响,考虑到运放的增益很高,则     

用于滤波器正反馈放大器的有源补偿电路

本文提出一种新颖的有源补偿电路,它适宜于取代用在许多低灵敏度单放大器的比奎特电路的正反馈放火器,试图扩展滤波器在高频的应用范围.新电路的主要优点是只需用一个电阻和一个运算放大器即可完成补偿。图1的正反馈放大器的转移函数由下式给出：     

一种用于GPS接收机的宽带、高增益变化范围的AGC设计

介绍了一种宽带、高增益变化范围的用于GPS接收机的模拟CMOS自动增益控电路(AGC)的设计.整个AGC环路用0.35μm CMOS工艺实现,包括可变增益运算放大器(VGA)、固定增益运算放大器(FGA)、增益控制电路和直流失调抑制电路.经过仿真验证AGC的最大增益可达80dB,增益变化范围是56dB,环路锁定时间为70μs.     

用运放制作1W/8Ω的功放

对于通用的运算放大器来说,由于输出电流只有10mA左右,所以无法用作低频功率放大器.但是如果在运算放大器的输出端接上一个由SEPP(Single Ended Push Pull)构成的电流缓冲电路,就可以充分地驱动8Ω扬声器.     

Improving the bandwidth gain-independence and accuracy of the current feedback amplifier

A high-performance current feedback amplifier circuit referred to as an operational current feedback amplifier is described in this paper. The technique employed involves the incorporation of the input circuit of the current feedback amplifier in the feedback loop of an operational amplifier to reduce the input impedance at the inverting terminal of the current feedback amplifier. The new circuit possesses the gain accuracy and bandwidth of the current feedback amplifier but realizes significant improvement in bandwidth accuracy and bandwidth gain-independence. Experimentally, using AD844s, an order of magnitude reduction in bandwidth variation with changing gain was achieved in the noninverting configuration and almost complete bandwidth invariance was realized in the inverting configuration.     

Enhancing output voltage swing in low-voltage micro-power OTA using self-cascode

It is shown how a self-cascode configuration can be profitably used in a micro-power operational transconductance amplifier (OTA), to enhance the output voltage swing, which eventually results in a power consumption reduction. A practical design example is proposed and used in order to discuss and quantify the circuit performance.     

Wideband translinear current convertor

A bipolar current-to-current convertor (CCCS) using a PNP-NPN translinear loop and two current mirrors is described. This convertor has a virtual earth input, and may be used to realise voltage-current conversion (VCCS). This convertor configuration enables us to obtain a wideband frequency response. The characteristics of a practical current source are presented.     

Active phase compensation of Op Amp VCCS structures

A generalized active compensated three-port voltage controlled current source (VCCS) is proposed. The compensation is affected by adding to the uncompensated VCCS another op amp and two resistors. The compensated VCCS (which may be used as an inverting or a noninverting VCCS) has a negligible phase error and an improved bandwidth.     

Highly linear amplifier for high gain applications

A novel amplifier structure that compensates nonlinearities by means of a special type of feedback is proposed. The high linearity performance is combined with a high gain that is unreachable with the conventional feedback structure. A practical configuration of the structure is given as an improvement over both a conventional feedback amplifier and a typical feedforward amplifier. Experimental results are provided to verify the high linear characteristic of the practical structure     

一种适用于高速高精度流水线ADC的放大器

本文提出了一种新颖的放大器结构.它由两部分组成:前面为跨导放大器,后面则是由电阻反馈形成的跨阻放大器,两种放大器的组合构成了具有高输入阻抗、低输出阻抗的电压放大器.与普通放大器不同的是,在我们设计的工作条件下,它输出端的极点几乎不受负载电容的影响.用该放大器作为预放大级,驱动一单级主放大器所构成的两级运放在负载电容为4pf的情况下实现了超过1GHz的增益带宽积,瞬态分析的结果表明它可以在10ns内达到0.01%的精度(闭环增益为8),而功耗仅有25mW,远低于同性能其他结构的放大器,非常适合作为高速高精度流水线模数转换器中的首级余量放大器使用.     

A differential-input,differential-output current mode operational amplifier

A current operational amplifier with differential input and differential output is described. The amplifier is based on the parallel connection of a CCII+ current conveyor and a CCII? current conveyor followed by a differential output transconductance gain stage. The performance of the amplifier is analysed and experimental results obtained from an implementation using standard operational amplifiers and current mirrors realized using transistor arrays are presented and compared to the theoretical analysis. It is concluded that the static small signal open loop gain and the frequency response matches the performance of conventional voltage operational amplifiers. The input offset and bias errors and the common mode rejection are shown to be strongly dependent on the matching accuracy of the current mirrors used in the conveyors. The proposed configuration can easily be integrated into a monolithic amplifier in either CMOS or bipolar technology.     

Low offset, high voltage class AB bipolar voltage-current converter

A new high voltage class AB bipolar voltage-current converter (VCCS), which features low offset voltage and is suitable for monolithic IC fabrication, is described. The architecture of the converter is particularly suited for the implementation of a precision VCCS with wide input and output voltage range. Some SPICE simulations and experimental results are also reported, which demonstrate the effectiveness of the proposed configuration     

Chopper stabilization of MOS operational amplifiers using feed-forward techniques

A monolithic chopper amplifier system has been developed that reduces the effective offset voltage of an NMOS operational amplifier to a few microvolts without compromising bandwidth. Internally, two amplifiers are used, connected in a switched feed-forward configuration. The system is realized in a standard silicon gate enhancement/depletion process.     

“模拟电子技术基础”中的运算放大器教学改革

本文根据"模拟电子技术基础"课程中关于运算放大器教学中普遍存在的问题,提出了基于工程应用背景下的教学理念,减少了对运算放大器内部电路的讲解,突出了对其等效模型的理解,加强了对运算放大器参数指标的认识,强化了运算放大器在实际应用电路中的具体要求。由此提高了对学生工程实践能力、自学能力的培养,取得了良好的教学效果。